DEAR DOCTOR K:
My mother had breast cancer, so I believe I’m at higher risk than are most women. Should I take medication to prevent breast cancer?
Without more details, I can’t give you a personal recommendation. But I can tell you about drugs that are available to prevent breast cancer and who, in general, should consider taking them.
There are different types of breast cancer. The most common type is “estrogen receptor-positive” (ER-positive). This type of breast cancer needs the hormone estrogen to grow.
Well-designed studies have shown that two drugs — tamoxifen and raloxifene — reduce the risk of ER-positive breast cancer. (Tamoxifen appears to be more effective than raloxifene.) These drugs are known as selective estrogen receptor modulators (SERMs). Please see the table for more information about tamoxifen and raloxifene:
Breast cancer prevention drugs
|Class||Generic name (brand name)||Recommended dose, duration||Effectiveness||Potential side effects|
|SERM||Tamoxifen (Nolvadex)||20 mg/day for five years||May lower breast cancer risk by up to 50%||Blood clots in the legs or lungs, uterine cancer, cataracts, menopause symptoms (hot flashes, night sweats, vaginal dryness)|
|SERM||Raloxifene (Evista)||60 mg/day for five years||May lower breast cancer risk by up to 40% (also protects bones in postmenopausal women)||Blood clots and uterine cancer (but lower risk than with tamoxifen), menopause symptoms (hot flashes, night sweats, vaginal dryness), weight gain|
|Aromatase inhibitor||Exemestane (Aromasin)||25 mg/day for five years||May lower breast cancer risk by up to 65%.||Menopause symptoms (hot flashes, night sweats, vaginal dryness), weakened bones|
So far, so good. The problem is that SERMs can cause side effects, some serious. These include increased risk of blood clots and hot flashes. Tamoxifen also increases the risk of uterine cancer and cataracts. The question is: For which women do the benefits of these drugs outweigh the possible side effects?
Late last year, the U.S. Preventive Services Task Force (USPSTF) issued guidelines on the subject. They recommended that physicians should offer to prescribe tamoxifen or raloxifene to women who are at high risk for ER-positive breast cancer and low risk for side effects.
Your doctor can estimate your breast cancer risk by taking several factors into account. These include your age, history of breast or ovarian cancer in a first-degree relative, and the age at which you first gave birth. Factors that decrease your risk for side effects include being younger than 50 years, having no risk factors for blood clots or stroke (such as being a smoker), and not having a uterus.
You can estimate your breast cancer risk with an online tool from the National Cancer Institute’s website: cancer.gov/bcrisktool. After you enter information about yourself, the tool gives you an estimate of your risk over the next five years, and over a lifetime.
I am not aware of any similar tools to estimate your risks from taking either tamoxifen or raloxifene. As a general rule, doctors generally advise against taking these drugs if you:
- Have had past serious blood clots requiring treatment;
- Are taking blood-thinning medicines such as warfarin (Coumadin) or heparin;
- Have high blood pressure, obesity or diabetes;
- Are a smoker;
- Are younger than 35 years old;
- Are between 35 and 60 years old, and not at increased risk for breast cancer;
- Are taking hormone replacement therapy or an aromatase inhibitor;
- Have had any type of uterine cancer.
In addition, women who are pregnant or planning to become pregnant, or who are currently breastfeeding, should generally avoid tamoxifen.